This post will continue with looking at workloads and evidence of overuse, by examining the end of the season games, and playoffs, and what effect it has on injury rates early the next season.

The below chart contains all running backs who played in all team games between weeks 12-17, with a couple of caveats. First, if a back missed only week 17, and he played in the playoffs, he was included. Also, between 1995-2001, there were a few backs that had bye weeks at the end of the year. Thus, we are not dealing with backs who had the same number of games, some could have five, some could have six. Thus, the players are divided by attempts/game, and not raw attempts, like yesterday.

This chart also does not separate out playoff participants from non-playoff participants (I'll discuss the playoff games shortly). Here are the injury rates for the early part of next season, sorted by average attempts per game over the last 6 weeks of the regular season. "GP" is the average number of games played the next season by players in that group. "SEI" represents "season ending injury" and is for all backs who had a season ending injury within the first 6 games of the following season. "INJ6" represents the running backs who missed at least 1 game due to injury in the first 6 games of the next season, but returned to play following the injury. If you add "SEI" and "INJ6", you will have the total percentage of players who missed at least one game out of the first six the following season. "PL15" represents all backs, among those who made it through the first 6 games of the next year healthy, who went on to play in at least 15 regular season games.

The pattern is similar to the early season pattern from the previous post. The groups between 19.0 and 22.9 attempts per game represent the peak in terms of average games played the next season. For the lower carry groups, the season ending injury rate is not high, but the players in these groups tend to miss some games early, and those who do not miss some games later at a higher frequency. The higher carry groups have increased season ending injury rates in the short term, but if they survive the early part of the next season without injury, they tend to remain healthy at a high rate.

Here are the players included in the above study, but sorted by games played in that year's postseason, rather than rushing averages:

When the players are sorted by playoff games played after the season, there is generally no effect on injury rates, with a couple of exceptions. As we have seen, higher workloads increase the risk of serious injury already. Extending the season in the playoffs is like a spark, and high workloads are the gas. Also, if a team is using a running back heavily in the final weeks of the regular season, they do not typically reduce that use in the playoffs, so we are generally seeing the overuse period extended.

Three running backs averaged 25.0 or more rush attempts per game over the final six weeks of the regular season, and then played in three or more playoff games. Those three are Terrell Davis (1998), Jamal Anderson (1998), and Jamal Lewis (2000). I do not need to spend much time discussing their well-known injuries. In short, all three blew out knees early the next year: Lewis before the season began, Anderson in game two, and Davis in game four. If we add in the 23.0-24.9 group, four more running backs played in at least three playoff games. Those backs were Emmitt Smith (1995), Dorsey Levens (1997), Corey Dillon (2004) and Shaun Alexander (2005). Emmitt played in 15 games the next season; the other three all suffered injuries early the next season. Both Dorsey Levens and Shaun Alexander had serious injuries early, had consecutive games missed, but did return later in the season. For Levens, it was nine games missed in a row with a knee injury. Alexander missed six consecutive games last season with a foot injury.

The other exception where extending the playoffs increased injury rates involved recently injured backs. I found thirty backs who played in at least 3 playoff games (and averaged at least 10 carries a game) in one post season since 1995. Of those thirty, six had missed at least one game in weeks 12-16 of the regular season, before returning in the playoffs. Of those six, five of them missed at least one game within the first six games of the next season, and none of them played in more than 13 games the next year. The six were Lamont Warren (1995), Bam Morris (1995), DeShaun Foster and Stephen Davis (2003), Antowain Smith (2003), and Brian Westbrook (2004). Of those, two suffered season ending injuries early--the Panthers' Davis and Foster. Davis played two games before knee injury ended his season. Foster played in four before a knee injury--having a 32 attempt game in week 2 probably did not help either.

In my opinion, it is not the raw number of carries that matters. I believe the key is the number of higher stress games a back endures over a period of time. I will refer to these as Increased Risk Games (IRG). For now, my educated guess in reviewing the data is that the cutoff to qualify for an IRG is around 25 rush attempts for an average, healthy starting running back. More research is needed in this area, as the number may be lower or slightly higher depending on other factors, such as age, recent injury history, or stamina/conditioning of the specific back.

The pro football reference database has regular season game by game data back to 1995, but the playoff database goes back to the start of the Super Bowl era. Going back to 1978, there were 74 player-seasons where a back had at least one IRG in a postseason. Ten of those 74 backs (13.5%) played in six or fewer games the next season. Four of them were already discussed--Lewis, Anderson, Terrell Davis, and Stephen Davis. Going back in time, the other six were Edgar Bennett (1996)-0 games, Greg Bell (1989)-6 games, Ickey Woods (1988)-2 games, Dan Doornink (1984)-6 games, Curt Warner (1983)-1 game, and Wendell Tyler (1979)-4 games. Rob Carpenter (1981) also played in less than 6 games the next season, but the next season was the strike-shortened 1982 season, and I could not find information on the reason for his missed games to know whether to include him.

Here are some other recent cases that were not previously discussed, or not included in the previous studies, but which also show the potential role IRG plays in increasing risk of injuries, beyond what simply knowing raw rushing attempt totals might tell us. I could have selected numerous others; I selected these to get a mix of different type players or players with different reputations.

Samkon Gado (2005): his 8 games/143 attempts might not seem excessive, but he had 4 IRG in the 6 games before his season-ending knee injury.

Deuce McAllister (2005): 82 carries through 4 games prior to ACL injury does not seem excessive, but two of the four games were IRG.

Clinton Portis (2003): Portis had 4 IRG in last 6 games, including 38 attempts in final game, before missing the final 2 games of the regular season with chest injury.

Lee Suggs (2003 and 2004): After being injured and little used all year, Suggs had 26 carries in week 17 of 2003. He missed first 3 games next season. He had back to back IRG at the end of 2004, including 38 attempts in week 16. Played in only two of first ten team games next season, and has had only 14 attempts last two seasons.

Duce Staley (2000): Staley's 79 carries through 5 games, and 326 carries in 16 games the previous year might not suggest overuse, if you were going by raw attempts. He closed 1999 with 2 of 4 IRG, and then had 26 attempts in game 1 of 2000. He went downhill quickly thereafter, and was done by week 5.

If you want to know how the regression Doug ran last year, and the research here can be reconciled, I believe, in a figurative sense, it is because of Samkon Gado and Lee Suggs. I am skeptical that prior historical workload has anything to do with injury risk. What matters is recent workload. In other words, Curtis Martin may have broken down in 2005 beyond what could be expected on age, due to workload over the second half of 2004, but I do not think what he did from 1995-2000 had any impact on whether he was going to break down or not. If Larry Johnson breaks down early in 2007, it will be because of what happened late in 2006, and have little to do with what happened late in 2005.

So, for Johnson, there is a glimmer of hope. If his workload is reduced next year, and he does not show signs of an injury early in the season, he is probably going to be okay (assuming no more IRG, an assumption not likely to be realized). I will close with my assessment of the top five injury risks early next season. The top one is probably not who you think it would be, in a season where the rush attempt record was broken.

Shaun Alexander-- Alexander came off missing six games due to the foot injury, and was immediately subjected to a workload greater than any of his career. Apparently, Holmgren thought he needed to be punished for missing games. Alexander had a whopping 220 carries over 8 games since week 12 last year, including 5 IRG. With his age, recent injury history, extremely high IRG rate, and rumors of the foot injury not being healed, Alexander has more red flags than the United Nations.

Larry Johnson-everyone knows about his record setting rushing totals last year. Unsurprisingly, then, he had 4 IRG in his last 7 games. His one saving grace is that he was not extended in the playoffs, and the Colts bottled him early and prevented him from adding to that IRG total.

Steven Jackson- through 13 games last year, Jackson was a model of how a top running back should be used to keep him healthy and productive. Jackson had zero IRG, as he consistently had games of between 18 and 22 attempts. Then, for whatever reason, he finished with 3 IRG in his last 3 games, including over 30 attempts in two of them, which places him squarely in the high risk category for developing an injury early in 2007. Linehan will have major regrets if Jackson's season is ruined due to work while playing out the string on a non-playoff year in 2006.

Rudi Johnson- Rudi closed with 3 out of 6 IRG. That alone might place him in the group. Couple that with his age beginning to get on the wrong side of prime running back age, his decline in ypc last year to 3.8, and the Bengals using a 2nd round pick on a running back, and I have my concerns.

Ladell Betts- Betts played backup most of the season, but closed with 3 out of 6 IRG, and 156 attempts in his last 6 games. He may not get enough attempts to make him as big a risk early, but he is still a risk to breakdown early.

Now, am I predicting any of these guys to definitely get hurt? No. When I say high risk, that means each of them have about a 15-25% chance of suffering a significant injury early in 2007, based on the historical data. But that is a significantly higher chance than other running backs, such as Joseph Addai or Reggie Bush, have of suffering a severe injury early in 2007.

This entry was posted on Thursday, July 12th, 2007 at 4:39 am and is filed under Fantasy, General, Statgeekery.
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I agree with Richie. I'd like to see a chart listing the percentage of backs at various levels of IRG in a given season who missed games or had a serious injury the following year. Ideally, one would adjust for age and other factors as well.

I will try to accomodate. Keep in mind, most of the running backs will not get a serious injury (probably about 85%). I would estimate starting running backs average about 20% of the games being increased risk games (IRG). To try to give you a sense, though, here are the recent starting careers of 8 of the most prominent high profile backs in the last few years. What I will do is list each year, followed by number of IRG games (including playoffs), and number of high risk periods (periods with 3+ games in short spans of 6 weeks or less), which I will denote as HR, plus a little commentary. If I didn't make a comment, assume no effect, at least in the short term:

ALEXANDER
2001-6 IRG, 1 HR, went thru 4 game stretch of 3.0 ypc right after HR, but did not miss games, before bouncing back at the end of season.
2002-3 IRG, 0 HR
2003-2 IRG, 0 HR
2004-6 IRG, 2 HR
2005-6 IRG, 2 HR, 2nd HR was end of season/playoffs, foot injury start of 2006.

To sum up, there were 31 HR periods for these elite backs. 5 experienced suspicious short term significant performance declines, but no missed games, 4 more missed some games soon after, and 3 suffered severe injuries that required substantial amount of missed games. So, it looks like 19/31 (61%) suffered no adverse effects from a High Use Period.